Airframes with high aspect ratio fixed wings, e.g., wings rigidly attached to a fuselage wherein a laterally extending length, or span, of the wing is much greater than a distance between its leading and trailing edges, or chord, can be reliable and efficient in forward flight. These airframes can have several disadvantages as well, including difficulty maneuvering at slow speeds and the need for runway or other runout for takeoff and landing. Prior attempts to address these issues have included airframes with tilting nacelles that house motors, engines, or other thrust producing components to better control an aircraft at slow speeds and allow for short takeoff and landing (STOL) or vertical takeoff and landing (VTOL) operation. In such configurations, however, high aspect ratio fixed wings can be detrimental. For example, long fixed wings can be difficult to maneuver during STOL or VTOL operation due to a large moment of inertia created by their mass being extended away from a center of gravity of the aircraft. Further, there can be significant aerodynamic drag from moving a wing in a manner that presents its largest surface area as a leading edge. Vertically-oriented wind gusts, such as downdrafts, etc., can also have significant impacts on long, fixed wings.
Other prior attempts to address issues with high aspect ratio fixed wing airframes have included tilting an entire wing assembly including engines or other thrust producing components about a span axis extending between wingtips. While such designs can aid in alleviating the above-described aerodynamic losses from moving a wing in a direction substantially normal to its intended angle of attack, they can still be difficult to maneuver due to the large moment of inertia of the extended wings. Further, the tilted wings can be impacted by horizontally-oriented wind gusts against the tilted surface area of the wings.
Prior configurations of both tilt-engine and tilt-wing airframes that can achieve STOL or VTOL operation also suffer from instability during transition from takeoff or landing configurations to forward flight configurations. Accordingly, such aircraft often exhibit bimodal operation envelopes and cannot stably or indefinitely operate at any speed between the takeoff or landing realm and the high-speed forward flight realm.
A further disadvantage of high aspect ratio fixed wing airframes is the need for substantial storage space at rest and substantial clearance during ground transport. Prior attempts to address these issues have included a variety of wing folding and tilting mechanisms. These mechanisms, however, are often tailored to ground storage or transport and are not operable during flight to enable, for example, vertical takeoff and landing, etc.
Accordingly, there is a need for improved airframes that provide efficient forward flight as well as vertical takeoff and landing. There is also a need for improved airframes that can smoothly and stably transition between such modes of operation.